Video image reading apparatus

Abstract

A video image reading apparatus stores video data from a reader of the video image of an original document and outputs the stored video signals as a standard television video signal by successively reading the video signals from the video memory in a timing relationship complying with a given standard television format. The present invention makes it possible to reduce the storage capacity of the video memory by comparing the lower-order bits of the video data from the video image reader with a reference data which cyclically changes and by adding a result of comparison to the higher-order bits to store the sum to the video memory.

What is claimed is: 
     
       1. A video image reading apparatus, comprising: means for reading the video image of an original document and for generating video image data based upon said read video image;   means for dividing said video image data from the video image reading means into higher-order bits and lower-order bits;   means for comparing the lower-order bits from the bit dividing means with a reference data which cyclically changes;   means for adding said comparison output data outputted from the comparing means to the higher-order bits from the bit dividing means and for generating added output data;   video memory for storing said added output data from the adding means as output video data; and   means for outputting the output video data stored in the video memory as a video signal equivalent to a standard television signal by successively reading the stored output video data in a timing relationship complying with a given standard television format;   wherein said video image data has a first number of bits and said video output data has a second number of bits and wherein said first number if larger than said second number.   
     
     
       2. A video image reading apparatus as defined in claim 1, wherein said video reading means is a line sensor comprising a plurality of photocells arrayed in a main scanning direction relative to the original document, the sensor being moved in a subsidiary scanning direction relative to said original document to read a two-dimensional video image. 
     
     
       3. A video image reading apparatus as defined in claim 1, wherein said comparing means respectively outputs a binary data of either a "1" or "0+ depending upon whether the lower-order bits from said bit dividing means are larger or smaller than the reference data. 
     
     
       4. A video image reading apparatus as defined in claim 1, wherein said reading means, said dividing means, and said video memory all use a common clock generator and said reference data cyclically changes under the timing of said clock generator. 
     
     
       5. A video image reading apparatus as defined in claim 1, wherein said first number of bits comprises 8, said second number of bits comprises 4, and said higher-order bits and said lower-order bits each comprises 4 bits. 
     
     
       6. A video image reading apparatus as defined in claim 1, wherein said adding means further comprises an overflow processing circuit.